In order to maintain proficiency in the use of firearms, it is common to engage in target practice on a training range. Traditionally, the primary concern on a training range has been the prevention of ricochets. Thus, ranges often use a large dirt berm behind the target to decelerate and trap the bullet.
In addition to preventing ricochets, considerable concern has recently been raised about the environmental impact of heavy metals (e.g., lead, tungsten, copper) contained within the bullet. Though a bullet fired into a mound of dirt is safe insofar as it is no longer a dangerous projectile, heavy metals within the bullet remain free to leach into the soil, thereby contaminating the environment. Thus, shooting ranges have begun to stress containment and removal of expended rounds in order to minimize environmental contamination.
Thus, current trends in bullet containment systems focus on two different types of systems. The first, often called a bullet stop and containment chamber, has a pair of plates that channel bullets toward an opening in a containment chamber. Inside the containment chamber are impact plates that slow the bullet to a stop. Rounds may then be reclaimed from the containment chamber. Unfortunately, such systems are relatively expensive and difficult to manufacture and maintain.
The second type of containment system is the bullet backstop or bullet trap system. Bullet backstops typically include a back plate made of steel inclined to the line of fire. On an upper surface of the back plate, a layer of material is disposed to provide a medium for decelerating and trapping bullets. This layer is several feet thick in the direction the bullet travels. The impact material is typically a resilient granular material. As a bullet impacts the material, it will decelerate sufficiently such that, if it does impact the back plate, any ricochet will be minimal. Rounds may periodically be mined from the impact material.
A number of bullet traps utilize rubber chunks or chips as the impact material. For example, U.S. Pat. No. 6,378,870 to Sovine (“the '870 patent”) teaches the use of relatively large rubber nuggets disposed along a plane inclined to the line of fire, while U.S. Pat. No. 5,848,794 to Wojcinski et al. (“the '794 patent”) discloses a similar bullet trap using relatively small rubber granules disposed along an inclined plane.
Though these systems trap the bullet and reduce impact hazards, they generally do nothing to stabilize them from an environmental standpoint while they remain in the trap. While some extant systems teach the use of stabilizing or passivating additives to minimize environmental hazards, they generally teach the use of powdered or granular additives. For example, U.S. Pat. No. 6,688,811 to Forrester (“the '811 patent”) teaches the use of a granular additive that is essentially a slow-release phosphate fertilizer added to the projectile impact area as suggested by the Environmental Protection Agency (EPA). These granular and powdered additives have a tendency to settle as the trap is vibrated by incoming fire or wash out when the trap is wetted. Either event has a deleterious effect on the concentration and distribution of buffering compound within the trap. Thus, there remains a need to either periodically replenish the additives or recover expended rounds from the bullet traps to prevent heavy metal leaching and associated environmental contamination.